This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. The focus of our study, that is the identification and characterization of a living example of arsenic-based life, is certainly a high risk but exceedingly interesting study as funded by the NASA NAI. Thus far we have used the arsenic-rich, hypersaline and highly alkaline waters of Mono Lake, CA to hunt for such an unusual organism. Our current status is that we have enriched for, isolated and identified (by 16s rDNA) a member of the gamma-Proteobacteria that are known to bioaccumulate arsenic. We confirmed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS) that under growth conditions in which ONLY 5 mM arsenate was amended to the medium and NO phosphate was added this strain has a As/P ratio of almost 7;however this strain can also grow with phosphate only and phosphate combined with arsenate leading to the reassuring As/P ratios of 0.001 and 0.010, respectively. In addition, we are currently measuring the uptake of radiolabeled 73As arsenate to confirm the rate of uptake under a variety of anionic nutrient conditions, but our data indicate that developing a comprehensive picture of the intracellular arsenic content and speciation of cells grown with and without arsenate or phosphate would greatly strengthen our story.